1. Field of the Invention
The present invention relates to a refrigerant cycle system for a vehicle, having a hot-gas bypass structure for directly introducing hot gas discharged from a compressor into an evaporator while bypassing a condenser. When the hot-gas refrigerant discharged from the compressor is directly introduced into the evaporator while bypassing the condenser, the evaporator is used as a radiator.
2. Description of Related Art
In a conventional refrigerant cycle system described in U.S. Pat. No. 5,291,941, a hot-gas bypass passage 118, through which refrigerant discharged from a compressor 110 is directly introduced into an evaporator 132 while bypassing a condenser 120, is provided, and a decompression unit 117 is disposed in the bypass passage 118. Further, in an air conditioning unit 130, a heater core 133 is disposed at a downstream air side of the evaporator 132. When temperature of engine-cooling water from an engine 112 is lower than a predetermined temperature in a heating mode, an electromagnetic valve 115 is closed and an electromagnetic valve 116 is opened, so that high-temperature gas refrigerant discharged from the compressor 110 flows into the evaporator 132 through the hot-gas bypass passage 118.
Further, a receiver 151 is disposed at a downstream side of the condenser 120, for separating refrigerant after passing through the condenser 20 into gas refrigerant and liquid refrigerant, and for storing surplus liquid refrigerant therein. On the other hand, an accumulator 135 is disposed between an outlet side of the evaporator 132 and a suction side of the compressor 110 so that separated gas refrigerant is sucked into the compressor 110.
However, in the conventional system, when a throttle diameter of a throttle passage for returning oil is made larger in the accumulator 135 for improving heating capacity in the heating mode, liquid refrigerant amount sucked into the compressor 110 in a cooling mode is increased, and cooling capacity is decreased in the cooling mode. That is, it is difficult to improve both the cooling capacity and the heating capacity.
In addition, in the conventional system, the hot-gas bypass passage 118 extends from a refrigerant discharge side of the compressor 110 in an engine compartment to a refrigerant inlet side of the evaporator 132 in a passenger compartment, and becomes longer. Therefore, a refrigerant pipe structure becomes complex, and it is difficult for the refrigerant cycle system to be mounted on a small space of a vehicle.
In view of the foregoing problems, it is an object of the present invention to provide a refrigerant cycle system having a hot-gas bypass structure, which improves both heating capacity in a heating mode and cooling capacity in a cooling mode.
It is an another object of the present invention to provide a refrigerant cycle system in which a size of a first gas-liquid separator provided in a low-pressure side can be reduced.
It is a further another object of the present invention to provide a refrigerant cycle system for a vehicle, in which a refrigerant pipe structure can be made simple and mounting performance on the vehicle can be improved.
According to the present invention, in a refrigerant cycle system where a heating mode and a cooling mode can be selectively switched in a heat exchanger, a first gas-liquid separator for separating refrigerant into gas refrigerant and liquid refrigerant and for introducing gas refrigerant into a compressor is disposed between a refrigerant outlet side of the heat exchanger and a refrigerant suction side of the compressor, and the first gas-liquid separator has a throttle passage for introducing a part of liquid refrigerant stored in the first gas-liquid separator into the compressor. Further, the condenser includes both first and second heat-exchanging units which are disposed in this order in a refrigerant flow direction, and a second gas-liquid separator disposed between the first heat-exchanging unit and the second heat-exchanging unit for separating refrigerant into gas refrigerant and liquid refrigerant. Because gas refrigerant within the second gas-liquid separator is changed on a saturated gas line of a Mollier diagram, a super-heating state of the refrigerant discharged from the compressor is determined by a heat-exchanging amount of the first heat-exchanging unit. In addition, because a compression process of refrigerant in the compressor is basically an isoentropic change due to adiabatic compression, a super-heating degree of refrigerant at the outlet of the heat exchanger can be controlled to a suitable value by suitably setting the heat-exchanging amount of the first heat-exchanging unit. Accordingly, in the cooling mode, the super-heating state of refrigerant at the outlet side of the heat exchanger can be forcibly set at a suitable super-heating degree by controlling the heat-exchanging amount of the first heat-exchanging unit. Therefore, in the cooling mode, even when a throttle opening degree of the throttle passage of the first gas-liquid separator is made larger, it can prevent liquid refrigerant amount sucked into the compressor from being increased. As a result, the throttle opening degree of the throttle passage can be made larger. In this case, in the heating mode, compression operation amount can be increased, and the heating capacity in the heating mode can be improved without reducing the cooling capacity. Accordingly, in the refrigerant cycle system, it is possible to improve both the heating capacity and the cooling capacity.
Further, because the second gas-liquid separator is also disposed between the first and second heat-exchanging units, a tank volume of the first gas-liquid separator can be made smaller. In the cooling mode, the first gas-liquid separator can be used only as a refrigerant passage where super-heating gas refrigerant from the heat exchanger flows. Only in the heating mode, the first gas-liquid separator has a gas-liquid separation function. Therefore, the size of the first gas-liquid separator can be greatly reduced, and mounting performance of the first and second gas-liquid separators on the-vehicle can be improved.
Preferably, the first heat-exchanging unit is disposed to cool and condense refrigerant discharged from the compressor, the second gas-liquid separator is disposed for separating refrigerant from the first heat-exchanging unit into gas refrigerant and liquid refrigerant and for introducing separated gas refrigerant into the second heat-exchanging unit, the second heat-exchanging unit is disposed for condensing gas refrigerant from the second gas-liquid separator, and a super-heating degree of refrigerant at a refrigerant outlet of the heat exchanger is controlled by the heat-exchanging amount in the first heat-exchanging unit. Therefore, in the cooling mode, the super heating degree of refrigerant at the refrigerant outlet of the heat exchanger can be suitably controlled.
Preferably, the first heat-exchanging unit and the second heat-exchanging unit are integrally constructed as an integrated member, and the second gas-liquid separator is constructed integrally with both the first and second heat-exchanging units. Therefore, the integrated condenser can be readily mounted on the vehicle.
Further, the first decompression unit is disposed at a position proximate to the condenser, a refrigerant outlet side of the first decompression unit and a refrigerant outlet side of the hot-gas bypass passage are joined to a single refrigerant pipe at a position proximate to the condenser, and the single refrigerant pipe is connected to a refrigerant inlet side of the heat exchanger. Therefore, a refrigerant pipe structure of the refrigerant cycle system can be made simple, and the refrigerant cycle system can be readily mounted on the vehicle.
On the other hand, in a refrigerant cycle system according to the present invention, a first gas-liquid separator for separating refrigerant into gas refrigerant and liquid refrigerant and for introducing gas refrigerant into a compressor is disposed between a refrigerant outlet side of a heat exchanger and a refrigerant suction side of a compressor, a second gas-liquid separator for separating refrigerant into gas refrigerant and liquid refrigerant is disposed in a branched refrigerant passage branched from a main refrigerant passage of a condenser, the first gas-liquid separator has a throttle passage for introducing a part of liquid refrigerant stored in the first gas-liquid separator into the compressor, and the second gas-liquid separator is disposed in such a manner that a liquid refrigerant amount stored in the second gas-liquid separator is adjusted in accordance with a super-heating degree of gas refrigerant discharged from the compressor. Therefore, the liquid refrigerant amount in the second gas-liquid separator can be adjusted in accordance with the super-heating degree of refrigerant discharged from the compressor, and the supper-heating degree of refrigerant at the refrigerant outlet side of the heat exchanger and the super heating degree of refrigerant discharged from the compressor can be adjusted. Accordingly, it can prevent a refrigerant amount circulating in the refrigerant cycle system from being insufficient, and a sufficient cooling capacity can be provided in the cooling mode. Further, because only a part of refrigerant in the condenser is introduced into the second gas-liquid separator while being branched from the main refrigerant passage of the condenser, a refrigerant-recovering operation can be effectively performed in a short time in the heating mode.